Modern portable communication devices (e.g., cell phones, PDAs, etc.) comprise a transmission chain configured to transmit radio frequency (RF) signals. The transmission chain typically may comprise a plurality of elements including a low noise amplifier, a modulation circuit (e.g., mixer), a filter, and a power amplifier. The power amplifier is configured to convert a modulated, filtered input signal with a small amount of energy into an output signal with a larger amount of energy. Efficiency and linearity are both factors in the performance of power amplifiers in modern wireless systems.
Adaptive digital pre-distortion (DPD) may be used to improve the quality of a signal by linearizing the non-linear response of a power amplifier. DPD is generally performed on a signal prior to modulation to generate a distorted version of the signal to be modulated. The distortion version of the signal has an inverse response of the power amplifier so as to account for distortion introduced by the power amplifier (i.e., so that the overall response of the power amplifier is linear). Therefore, the pre-distortion removes/reduces amplitude (AM/AM) and phase (AM/PM) non-linearities introduced by the power amplifier.